What makes Amazon app store and f-droid not first class?

No automatic software updates.

With my current android phone, I have deliberately limited what I put on it. I got so sick of update churn.

Together with app owners selling out to malware types, and I see a lack of updates as a blessing.

I want to buy an app version and use that app version until I decide otherwise.

Ideally, when I run an app, inform me there is an update, let me know the benefits, and let me decide if I want to install or not, before or after using the app on this occasion.

A very fair opinion, in just the same way, many iOS users see the single store model to be a feature not a bug.

I'd say it's a Google Play and specific deals limitation, not an Android limitation.

On a OnePlus phone I can easily activate root access and install f-droid as root which enables full updates handling.

It’s a limitation that applies to almost all Android users.

Clicking an f-droid notification and then "update all" is fine by me.

It's much better than having no alternative store at all, and installing things via adb commands.